U.S. patent number 8,574,791 [Application Number 13/009,347] was granted by the patent office on 2013-11-05 for method for production of a solid oxide fuel cell (sofc).
This patent grant is currently assigned to Robert Bosch GmbH. The grantee listed for this patent is Alexander Bluthard, Uwe Glanz, Benjamin Hagemann, Erhard Hirth, Harald Maus, Gudrun Oehler, Raphaelle Satet, Leonore Schwegler. Invention is credited to Alexander Bluthard, Uwe Glanz, Benjamin Hagemann, Erhard Hirth, Harald Maus, Gudrun Oehler, Raphaelle Satet, Leonore Schwegler.
United States Patent |
8,574,791 |
Maus , et al. |
November 5, 2013 |
Method for production of a solid oxide fuel cell (SOFC)
Abstract
A method for production of a solid oxide fuel cell (SOFC) (1),
having an electrolyte body (10) with a tubular structure, wherein
at least one internal electrode (11) and one external electrode
(12) are applied to the tubular electrolyte body, with the method
having at least the following steps: provision of an injection
molding core (13) on which at least one interconnector material
(14) and the internal electrode (11) are mounted, arrangement of
the injection molding core (13) in an injection mold (25a, 25b),
injection molding of an electrolyte compound (10a) in order to form
the electrolyte body (10), and removal of the injection molding
core (13) in the form of a casting process with a lost core.
Inventors: |
Maus; Harald (Sindelfingen,
DE), Glanz; Uwe (Asperg, DE), Satet;
Raphaelle (Tilburg, FR), Oehler; Gudrun
(Stuttgart, DE), Schwegler; Leonore (Stuttgart,
DE), Hagemann; Benjamin (Gerlingen, DE),
Bluthard; Alexander (Stuttgart, DE), Hirth;
Erhard (Ellhofen, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Maus; Harald
Glanz; Uwe
Satet; Raphaelle
Oehler; Gudrun
Schwegler; Leonore
Hagemann; Benjamin
Bluthard; Alexander
Hirth; Erhard |
Sindelfingen
Asperg
Tilburg
Stuttgart
Stuttgart
Gerlingen
Stuttgart
Ellhofen |
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A |
DE
DE
FR
DE
DE
DE
DE
DE |
|
|
Assignee: |
Robert Bosch GmbH (Stuttgart,
DE)
|
Family
ID: |
43759446 |
Appl.
No.: |
13/009,347 |
Filed: |
January 19, 2011 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20110177434 A1 |
Jul 21, 2011 |
|
Foreign Application Priority Data
|
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|
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Jan 19, 2010 [DE] |
|
|
10 2010 001 005 |
|
Current U.S.
Class: |
429/535; 264/279;
264/262 |
Current CPC
Class: |
B28B
7/342 (20130101); H01M 8/124 (20130101); H01M
8/1213 (20130101); H01M 8/004 (20130101); B28B
1/24 (20130101); H01M 2008/1293 (20130101); Y02P
70/50 (20151101); Y02E 60/50 (20130101) |
Current International
Class: |
H01M
8/12 (20060101); B29C 45/14 (20060101) |
Field of
Search: |
;429/497,535
;264/262,279 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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60123840 |
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May 2007 |
|
DE |
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0932214 |
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Jul 1999 |
|
EP |
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Other References
N Stelzer, R. Zauner, W. Grienauer, L. Baca, u.a.: "Miniaturisierte
keramische Hochtemperatur Brennstoffzellen Komponenten",
www.fabrikderzukunft.at, Jan. 24, 2007, pp. 1-64, XP002630265.
cited by applicant.
|
Primary Examiner: Kalafut; Stephen J.
Attorney, Agent or Firm: Michael Best & Friedrich
LLP
Claims
The invention claimed is:
1. A method for production of a solid oxide fuel cell (SOFC) (1),
having an electrolyte body (10) with a tubular structure, wherein
at least one internal electrode (11) and one external electrode
(12) are applied to the tubular electrolyte body, the method
comprising: providing an injection molding core (13) on which at
least one interconnector material (14) and the internal electrode
(11) are mounted; arranging the injection molding core (13) in an
injection mold (25a, 25b); injection molding an electrolyte
compound (10a) in order to form the electrolyte body (10); and
removing the injection molding core (13) in the form of a lost core
technique.
2. A method according to claim 1, characterized in that the
injection molding core (13) is removed by means of a thermal
process.
3. A method according to claim 1, characterized in that the
injection molding core (13) is formed of a plastic material.
4. A method according to claim 1, characterized in that the
injection molding core (13) is formed with a conical external
contour, such that a first end (15) with a large diameter and a
second end (16) with a small diameter of the injection molding core
(13) are formed, wherein the second end (16) with the small
diameter forms the holding end of the tubular electrolyte body (10)
on a base body (17).
5. A method according to claim 1, characterized in that the
interconnector material (14) and/or the internal electrode (11)
are/is applied to the injection molding core (13) by means of a
printing process.
6. A method according to claim 1, characterized in that the
interconnector material (14) and/or the internal electrode (11)
are/is applied to a carrier film (20), which is arranged on the
injection molding core (13) before the injection molding of the
electrolyte compound (10a), such that the electrolyte compound
(10a) is connected to the internal electrode (11) on the carrier
film (20) when the electrolyte compound (10a) is injection
molded.
7. A method according to claim 6, characterized in that the
interconnector material (14) is applied to the carrier film (20) in
layers (21), and the internal electrode (11) is then applied.
8. A method according to claim 7, wherein the layers (21) of the
interconnector material (14) extend to a different width over the
length of the injection molding core (13) in the longitudinal
direction, and form free areas (22).
9. A method according to claim 8, characterized in that the free
areas (22) are filled with filling layers (23).
10. A method according to claim 1, characterized in that the
injection molding core (13) has grooves (18) into which the
interconnector material (14) is introduced, in order to form an
interconnector layer (14) which has a structure.
11. A method according to claim 1, characterized in that the
interconnector material (14) is applied with a small thickness in
the area of the first end (15) and with a large thickness in the
area of the second end (15), such that the interconnector material
(14) has a conical internal shape.
12. A method according to claim 1, characterized in that, after the
electrolyte body (10) together with the internal electrode (11) and
the interconnector material (14) have been removed from the mold,
the external electrode (12) is fitted to the tubular electrolyte
body.
13. A method according to claim 1, characterized in that the
injection molding core (13) is formed of a plastic material,
wherein the thermal process for removal of the injection molding
core (13) is carried out by burning out the plastic material.
14. A method according to claim 1, characterized in that the
interconnector material (14) and/or the internal electrode (11)
are/is applied to the injection molding core (13) by means of a
web-fed printing process or a screen printing process.
15. A method according to claim 1, characterized in that the
injection molding core (13) has grooves (18) into which the
interconnector material (14) is introduced, in order to form an
interconnector layer (14) which has a web structure (19) or a grid
structure.
16. A method according to claim 1, characterized in that the
interconnector material (14) is applied with a small thickness in
the area of the first end (15) and with a large thickness in the
area of the second end (15), such that the interconnector material
(14) has a conical internal shape, and compensates for the conical
shape of the injection molding core (13), such that the
interconnector material (14) has an approximately cylindrical
external shape.
17. A method according to claim 1, characterized in that, after the
electrolyte body (10) together with the internal electrode (11) and
the interconnector material (14) have been removed from the mold,
the external electrode (12) is fitted and is subsequently burnt
in.
18. A method according to claim 8, characterized in that the free
areas (22) are filled with glassy carbon layers (23).
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method for production of a solid
oxide fuel cell (SOFC) having an electrolyte body in tubular form,
wherein at least one internal electrode and one external electrode
are applied to the electrolyte body.
Solid oxide fuel cells (SOFC) with a ceramic electrolyte body form
a high-temperature variant of fuel cells. They are operated at
600.degree. C. to 1000.degree. C., and in the process provide very
high electrical efficiencies of up to about 50%. In principle,
solid oxide fuel cells are subdivided into two main variants: one
variant is formed by a tubular shape of the electrolyte body which,
according to a further variant, can be bounded, by a flat, planar
form. In this case, it is necessary to fit the internal and
external electrodes to the wall of the electrolyte body during the
method for production of a solid oxide fuel cell based on the
tubular variant. For this purpose, it is known for the electrode
which is arranged on the inside of the electrolyte body, generally
in the form of the anode, around which the fuel gas flows, to be
applied as a coating on the inner wall of the electrolyte body. In
this case, the electrolyte body is preferably extruded.
In addition to the mounting of the electrodes on the finished
electrolyte body, so-called interconnectors are applied flat to the
electrodes in order to make contact with them, in which case
fitting on the inside of the electrolyte body frequently leads to
problems. Metallic interconnectors are known, which are composed of
a material with a high chromium content, in order to obtain
adequate corrosion resistance, combined with adequate electrical
conductivity, on the basis of the high operating temperatures. The
chromium-oxide layer which is formed during operation of the fuel
cell in this case has a negative effect on the cathode material,
and can lead to premature aging of the fuel cell. In contrast,
ceramic interconnectors for making electrical contact with the
electrodes are known in the planar form, but have not previously
been used for tubular solid oxide fuel cells. Because the
electrolyte bodies are very thin, there are major problems
associated with fitting ceramic interconnectors to the inner wall
of the electrolyte body. The problem results in particular from the
thin walls since, for example, the electrolyte body preferably has
a wall thickness of about 200 .mu.m, in which case the porous anode
on the inside of the electrolyte body must be coated with a ceramic
interconnector layer. For cost reasons, the electrodes themselves
must likewise be made thin, for example with a thickness of 50
.mu.m. Furthermore, the interconnector layer must likewise be
highly porous, with further advantages being obtained from the
interconnector material on the surface of the electrolyte body
having a thickness which varies over the longitudinal extent of the
electrolyte body.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to overcome the
disadvantages mentioned above relating to the production of a solid
oxide fuel cell, and to provide a method for producing an
electrolyte body, as well as the electrodes and corresponding
interconnector layers which are required on the inside and/or
outside of the electrolyte body, in a simple manner.
The invention includes the technical teaching that the method for
production of a solid oxide fuel cell comprises at least the steps
of provision of an injection molding core on which at least one
interconnector material and the internal electrode are mounted,
with the method furthermore comprising the arrangement of the
injection molding core in an injection mold, the injection molding
of an electrolyte compound in order to form the electrolyte body,
and the removal of the injection molding core in the form of a
casting process with a lost core.
The invention is in this case based on the idea that a ceramic
injection molding process is used to produce the electrolyte body,
in which the interconnector material and the internal electrode are
already arranged in the injection molding step such that they can
form a connection to the electrolyte body. In this process, an
injection molding core is arranged centrally in an injection mold
such that a tubular cavity is formed into which the electrolyte
compound is injected in order to form the electrolyte body. Since
both the interconnector material and the internal electrode have
already been applied to the injection molding core, the electrolyte
compound can form a connection to the inner electrode, such that is
subsequently necessary to remove the injection molding core from
the electrolyte body and from the internal electrode. The
interconnector material is applied to the injection molding core
before the application of the material to form the internal
electrode, such that the electrolyte compound can form a connection
to the material of the internal electrode.
The injection molding core can advantageously be removed by means
of a thermal process, and preferably by means of a lost core
technique when the electrolyte body is being injection molded. The
principle of destroying the shaping components for casting of a
workpiece during removal from the mold is referred to as a lost
core process, which can be used in the present case. The thermal
removal of the injection molding core can be carried out during a
sintering process, to which the electrolyte body together with the
interconnector material and the internal electrode are passed after
the injection molding process.
The injection molding core can advantageously be formed from a
plastic material, wherein the thermal process for removal of the
injection molding core is preferably carried out by burning out the
plastic material from the electrolyte body.
The injection molding core may be formed with a conical external
contour, such that a first end with a large diameter and a second
end with a small diameter of the injection molding core are formed,
wherein the second end with the small diameter constitutes the side
of the electrolyte body which forms the holding end of the tubular
electrolyte body on a base body. If the interconnector material
and/or the internal electrode are/is now applied to the injection
molding core by means of a printing process, in particular by means
of a web-fed printing process or a screen printing process, then
the application can be carried out such that a cylindrical overall
body is produced after application of the interconnector material
and the material of the internal electrode. This results in an area
of the interconnector material which has a greater wall thickness,
with this area being used to subsequently make electrical contact
with the internal electrode, because the highest current density
occurs at the contact end of the interconnector material. This
allows the thickness of the interconnector material to be matched
to the current density over the length of the electrolyte body.
According to a further advantageous embodiment of the method
according to the invention, the interconnector material and/or the
internal electrode are/is applied to a carrier film, which is
arranged on the injection molding core before the injection molding
of the electrolyte compound, such that the electrolyte compound is
connected to the internal electrode on the carrier film when the
electrolyte compound is injection molded.
The interconnector material can advantageously be fitted to the
carrier film in layers, with the internal electrode being fitted
only after this has been done. If the layers of the interconnector
material are fitted with a different width over the length of the
injection molding core, then free areas are formed which can be
filled with filling layers, in particular with glassy carbon
layers. A large number of layers fitted one on top of the other and
with a different width create a variable-thickness interconnector,
whose thickness increases in the direction for making contact with
the interconnector, since the current density is highest here. The
electrolyte body can be held on a base body via a flange, via which
contact is made with the interconnector. In consequence, more
layers of interconnect material are applied to the carrier film in
the direction facing the flange when the fuel cell is complete, and
in consequence in the direction for making contact. Filling layers,
in particular glassy carbon layers, can be applied to the carrier
film in order to fill the free areas which result from a reduced
number of layers applied. Since layers of interconnector material
are initially not applied to the carrier film over the entire
length corresponding to the length of the injection molding core,
the filling layers are applied adjacent to the individual layers of
the interconnector material. In consequence, a next layer of
interconnector material can also be applied above a filling layer.
Once the layers of interconnector material have all been applied,
the material to form the internal electrode is then applied.
According to a further advantageous embodiment, the injection
molding core may have grooves into which the interconnector
material is introduced, in order to form an interconnector layer
which has a structure, preferably a web structure or a grid
structure. By way of example, the interconnector material can be
introduced into the grooves in the injection mold by a wiper. In
consequence, the interconnector forms a matrix structure on the
electrode, in order not to cover it completely. The number of
grooves can advantageously be increased over the length of the
injection molding core in one direction in the structure, in order
to form a larger line cross section in the direction in which
contact will later be made with the interconnector, in order to
carry the greater current density.
The interconnector material may be applied with a small thickness
in the area of the first end and with a large thickness in the area
of the second end, such that the interconnector material has a
conical internal shape, and preferably compensates for the conical
shape of the injection molding core, such that the interconnector
material has an approximately cylindrical external shape. In this
case, the grooves in the injection molding core may also have a
different depth, which increases in the direction in which contact
will later be made with the interconnector.
According to a further method step, after the electrolyte body
together with the internal electrode and the interconnector
material have been removed from the mold, the external electrode is
fitted, and is preferably subsequently burnt in. The external
electrode can also be provided with an interconnector material
which can be applied after the electrolyte body has been removed
from the injection mold, in which case the external electrode and
an interconnector which is provided on the outside can also be
applied in the same manner to that on the inside of the electrolyte
body, based on the principle of film insert molding. In particular,
the principle of film insert molding can be provided both from the
direction of the injection molding core and from the direction from
the inside of the injection mold for spraying the electrolyte
body.
BRIEF DESCRIPTION OF THE DRAWINGS
Further measures which improve the invention will be described in
more detail in the following text together with the description of
one preferred exemplary embodiment of the invention, with reference
to the figures, in which:
FIG. 1 shows a schematic view of one exemplary embodiment of the
present invention,
FIG. 2 shows a further view of one exemplary embodiment of the
present invention with a conical injection molding core,
FIG. 3 shows a schematic view of interconnector material being
applied in layers on a carrier film,
FIG. 4 shows the schematic view of an electron with interconnector
material applied in strips, in a developed form,
FIG. 5 shows a perspective view of an electrolyte body with an
internal electrode and an external electrode, in each case with
interconnector material applied,
FIG. 6a shows one exemplary embodiment of an injection molding core
provided with grooves,
FIG. 6b shows the injection molding core as shown in FIG. 6a, with
interconnector material having been introduced into the grooves in
the injection molding core by means of a wiping process, and
FIG. 6c shows the view as shown in FIG. 6b, with material for
forming an internal electrode having been applied externally onto
the injection molding core, and with the interconnector material
having been introduced.
DETAILED DESCRIPTION
FIG. 1 shows a schematic view of one exemplary embodiment of the
method for production of a solid oxide fuel cell 1, as is
illustrated in perspective form in FIG. 5. First of all, FIG. 1
shows a cross section through an injection mold, which has a first
mold element 25a and a second mold element 25b. The mold elements
25a and 25b can move with respect to one another, and can be moved
apart from one another in order to remove an injection-molded
electrolyte body 10 from the mold. The electrolyte body 10 is in
the form of an electrolyte body that is closed at the ends, and
therefore has a cap 24. According to one possible embodiment for
production of the electrolyte body 10, this may be in the form of a
single part, such that the tubular, cylindrical section of the
electrolyte body 10 can be produced by injection of an electrolyte
compound 10a into the injection mold, in which case the cap 24 can
also be produced by the electrolyte compound 10a itself in the
injection mold. On the inside, the injection mold has an injection
molding core 13 which is illustrated merely by way of example as a
hollow core, in order to minimize the mass of the injection molding
core 13 which has to be removed by burning out once the injection
molding process has been completed. On the outside, an
interconnector material 14 is first of all applied to the injection
molding core 13, with the lower face having a large thickness which
decreases in the direction of the cap 24 of the electrolyte body
10. An internal electrode 11 is applied to the interconnector
material 14 and forms a direct connection with an electrolyte mass
10 when the latter is injected. When the electrolyte body 10 that
has been formed in this way is removed from the injection mold, and
the injection molding core 13 has been removed by a thermal process
from the inside of the electrolyte body 10, preferably by a thermal
process, then an electrolyte body 10 is produced having an internal
electrode 11 and an interconnector material 14 which makes contact
with it. At the same time, the interconnector material 14 is
already thicker at the second end 16 of the electrolyte body 10
than at the first end 15 since the subsequent contact will be made
at this end, and a higher current density must therefore be taken
into account.
FIG. 2 shows schematic views of the configuration of the coatings
on a carrier film 20, with the carrier film 20 being adjacent to
the internal electrode 11 in the upper illustration while, in
contrast, the carrier film 20 is illustrated in the lower
illustration as being adjacent to layers 21 of interconnector
material. The principle of film insert molding can therefore be
implemented, with the film being applied with the layer structure
to the injection molding core 13.
According to the upper illustration, the carrier film 20 is first
of all coated with the internal electrode 11, with layers 21 of
interconnector material then being applied to the internal
electrode 11. The layers 21 of the interconnector material are
shown with different extents, thus resulting in a free area 22
which is then filled with a filling layer 23, for example composed
of glassy carbon layers 23. The electrolyte compound 10a is then
sprayed on in order to form the electrolyte body 10, such that the
electrolyte compound 10a can make a firm, integral connection to
the internal electrode 11.
The carrier film 20 may be filled over the area, such that it can
be placed around the cylindrical injection molding core 13. It is
particularly advantageous for the carrier film 20 to be preformed
in the form of a sleeve or flexible tube, such that the sleeve or
the flexible tube can be placed, with the layers 11 and 21 or 23
applied to it, over the injection molding core 13.
The carrier film 20 can likewise also be removed by means of a
thermal process by removing the injection molding core 13 after the
injection molding step. This results in an electrolyte body 10 with
an applied internal electrode 11 and an interconnector formed from
layers 21. In order to obtain a cylindrical overall shape, the
filling layers 23 are provided at the points which the remaining
layer thicknesses of the layers 21 fill before the interconnector
material.
FIG. 4 shows a development of a carrier film 20 which may already
be fitted with an internal electrode (11, not illustrated) on the
upper face. The interconnector material 14 is applied in a strip
form, with the strips of the interconnector material 14 preferably
extending in the longitudinal direction of the electrolyte body 10,
and therefore in the longitudinal direction of the injection
molding core 13. FIG. 4 shows a development in the form of a
flattened-out illustration, in which the carrier film 20 can
preferably form a flexible tube with a circular cross section. The
strips of the interconnector material in consequence run at regular
distances from one another in the longitudinal direction of the
electrolyte body 10.
FIG. 5 shows a perspective view of a solid oxide fuel cell 1 which
has an electrolyte body 10 which forms the basic structure of the
fuel cell 1 and is closed at the top by a cap 24, in order to form
the solid oxide fuel cell 1 as a fuel cell which is closed at one
end. The solid oxide fuel cell 1 is mounted on a base body 17, at
the same time showing contact elements 26 for making contact with
the internal electrode 11, and a contact element 27 for making
contact with the external electrode 12. Interconnector material 14
is furthermore shown both on the inside, having a web structure 19
which is formed in strips by the interconnector material 14, as is
illustrated in FIG. 4. The external electrode 12 is likewise shown
with a web structure. Because the solid oxide fuel cell 1 has a
closed structure, it has an opening 28 for the fuel gas flow on the
side of the base body 17.
FIG. 6a shows one exemplary embodiment of an injection molding core
13 which is illustrated in the form of a cross section, and has
grooves 18 distributed uniformly over the circumference. As can be
seen from FIG. 6b, the grooves 18 can be filled with interconnector
material 14, in which case, by way of example, the interconnector
material 14 can be introduced into the grooves 18 by means of a
wiping process. FIG. 6c shows that the internal electrode 11 has
been applied after the application of the interconnector material
14, for example by a web-fed printing process or a screen printing
process. FIG. 6c therefore shows an injection molding core 13 with
the respective coating which, without the principle of film insert
molding, and in consequence without a carrier film 20, allows
electrolyte compound 10a to be injection molded into a mold, in
which case the electrolyte compound 10a can form an integral
connection to the internal electrode 11. During a subsequent
burning process, both the ceramic electrolyte body 10 and the
respective coatings 11 and 14 can be burnt in and hardened.
The embodiment of the invention is not restricted to the preferred
exemplary embodiment indicated above. In fact, a number of variants
are feasible which also make use of fundamentally different types
of embodiment from the described solution. All features and/or
advantages which result from the claims, the description or the
drawings, including design details, physical arrangements and
method steps, may be significant to the invention both in their own
right and in widely differing combinations.
* * * * *
References